Rotating parts such as wheel axles, shafts, vehicle wheels, machine tool parts and similar items are often monitored to determine particular parameters such as their temperature, internal pressure, portions, expansion, force and so on. Parameters of this sort can be measured by means of appropriate sensors. These applications meet difficulty when passing the values measured by sensors attached to rotating parts, such as those mentioned above, to the outside. Transmission along wires is not possible, particularly under circumstances where the parts do not move predictable, restricted distances in some direction. Certainly it is possible to exploit sliding contacts on parts that rotate slowly. Sliding contacts, however, have the disadvantage that they are subject to wear as a result of the constant friction, and that at high speeds of rotation the reduction in contact pressure leads to inadequate contact quality. Specially designed contacts can indeed provide secure contact pressure, but this brings high costs with it.
For this reason the method of transmitting signals from a measuring sensor on rotating parts by radio has been known for some years. Radio techniques, however, also require a power supply, and in the absence of contacts to transmit electronic signals, an independent power supply is necessary. Batteries, accumulators or similar devices represent obvious solutions.
Providing the energy by means of batteries, accumulators or similar devices is, for straightforward cases, an entirely practical solution. Batteries and accumulators are often unsuitable, however, if access to the sensor is difficult, or if the measured parameter has relevance to the safety of operation of the rotating part. The particular disadvantage is that, in the event of a sudden drop in the supply voltage, i.e. of the battery voltage, transmission from the measuring sensor can no longer be reliably assured, which may mean that safety-relevant information is no longer made available.
For this reason, the idea of providing an independent energy generator has already been considered. Generally speaking, solutions that exploit solar cells or other more or less usual generating methods are plausible. DE 102 59 056 A1 describes the structure of an electromechanical vibration converter, in which an oscillating weight is positioned on an oscillating arm that is located on a rotating element in such a way that the oscillating arm is aligned parallel to the axis of rotation. One side of the oscillating arm is fixed to the rotating part, and the oscillating mass is at the other end. The rotary movement causes the mass to oscillate whenever the axis of the rotation is not aligned with the direction of gravity. Because, as a result of the rotation, the oscillating mass is pulled in different directions at different times by gravity, oscillation develops. This is particularly encouraged if there is no opposing force. The oscillating mass now drives an electromechanical energy converter, generating an electrical oscillation from the mechanical oscillating movement. The disadvantage of this arrangement, however, is that as the speed of rotation increases, centrifugal force pulls the oscillating mass out of its path, preventing the oscillation.